The present invention relates to a workpiece clamping device employed, for instance, at a station in a transfer machine. More particularly, the invention relates to an improved workpiece clamping device which controls operating cylinders used to clamp and support workpieces of different sizes on a workpiece mounting jig.
In a conventional workpiece clamping device of the same general type to which the invention pertains, in order to clamp, for instance, workpieces of different heights or to change the number of operating cylinders, it is necessary to change the pivot points of the workpiece clamping arms according to the heights of the workpieces. Furthermore, it is necessary to change the coupling points of the operating cylinders which are coupled to the workpiece clamping arms. In addition, the work system must be reconfigured; for instance, the positions and the number of detectors constituting limit switches and dogs for controlling the advancement, clamp and over-stroke positions of the operating cylinders must be changed.
In the case of a conventional detector used for detecting the operative positions of operating cylinders, it is necessary to provide at least two limit switches and two dogs, and addition of operations cannot be made without increasing the numbers of limit switches and dogs. As a result, the conventional workpiece clamping device suffers from the difficulties that it occupies a relatively large installation space, it has a high manufacturing cost, and is difficult to maintain.
In the case where a workpiece clamping device in a transfer machine or the like of a type which has a mounting device for inclining or turning a secured workpiece has limit switches and dogs for each operating clyinder, the workpiece clamping device requires intricate electrical wiring. In the case where limit switches and dogs are provided on the stationary bed, the positions thereof are fixed. Furthermore, if a workpiece clamping device detects clamping conditions from the operating pressure of the operating cylinders, the positions of the operating cylinders cannot be detected simultaneously therewith.
As described above, in the case where, for instance, workpieces of different heights are machined while clamping them with the same workpiece clamping device, the reconfiguration required in the work system, such as changing the pivot points of the workpiece clamping arms and changing the control device for the operating cylinders according to the heights of the workpiece to be machined, are considerably intricate, and as a result the work efficiency with such a system is considerably low.